The present invention relates to a photoconductor for use in an electrophotographical copier or printer which uses as its light source a gas laser, laser diode, light-emitting diode, liquid crystal, CRT, or the like, and which, more particularly, comprises a conductive base on which a carrier transport layer, a carrier generation layer, and a surface protective layer are formed.
The light source of an electrophotographic copier or printer uses a single wavelength of electromagnetic radiation in the range of about 630 to 800 nm, which enables copied information to be transferred, stored and edited. In order for the photoconductor to respond to light of such long wavelength, a function-separating type multilayer photoconductor is used. Such a photoconductor comprises a carrier generation layer of a selenium-tellerium alloy which responds to electromagnetic radiation of such long wavelengths; a carrier transport layer of selenium-arsenic (Se-As) alloy which conveys the carriers produced in the carrier generation layer; and a surface protective layer of Se-As alloy which provides excellent resistance to chemicals, printing, and heat, and thus protects the carrier generation layer form external stress.
In an electrophotographic printer or copier equipped with such a photoconductor, the photoconductor is first electrically charged to provide a uniform electrostatic charge to its surface. The charged surface is then exposed to light to form an electrostatic latent image. A developing device supplies toner to the latent image to create a toner image, which is then transferred to paper by heat or pressure.
The use of the Se-As alloy in the surface protective layer protects the carrier generation layer from external stress caused by printing and heating operations. While this resistance is improved by a proportionate increase in the amount of arsenic in the surface protective layer, such an increase will, at the same time, have negative effects, such as reducing the rate at which the surface charge is retained, and causing deterioration of the ability of the surface layer to resist fatigue.
A further problem in the prior art devices exists with respect to surface potential. Generally, photoconductors used in printers and copiers are positively charged (except for OPC photoconductors). However, though the photoconductor undergoes repeated positive charging, the surface potential drops unfavorably. After carriers are generated inside the carrier generation layer, positive holes move away from the surface and toward the substrate. Simultaneously, electrons are transported toward the surface. If these elections become trapped in the surface protective layer, negative space charges are produced, thus lowering the surface potential.
Further adding to a decrease in surface potential is the ease by which electrons can move to the surface. Where, as here, the band gap of the surface protective layer is relatively narrow (about 2.0 eV for amorphous selenium), there is little resistance to electron movement.